Monday, May 30, 2005

Photos to Follow

I worked on every day of this long holiday weekend. Despite this, I had time to get a little work done in the shop. No photos yet, but soon.

The first major task was to mount the left chain stay to the bottom bracket on Sarah's bike. I choose to work off my drawings and pin the joint. What made this difficult was that I had to bend the BB socket down 8.5 degrees. This is, after all, a kids bike on 20" wheels.

I wasn't too sure about doing this, and I'm still not entirely sure that the main shell of the BB didn't get bent (next time I'll have to get some old BB cups and mount them during the bending process). I began by elongating the socket with the die grinder. I didn't want to use this as my primary method, but did want things to be a little loose to begin. I mounted the BB in my vice between to pieces of 3/8" plywood and tightened it down. Then I put the stay into the socket and pulled down.

I was concerned about bending the stay instead of the socket, but needn't have been. The end inside the BB shell hit the top of the shell and bent down some, but that part needed to come off anyway. So, I worked the stay out, trimmed back the inside end, and set it back in place to check against the drawing. A couple of more smaller pulls and I had it made. Then I drilled the BB shell for two pins, close to 180 degrees apart, fluxed everything up, fit the stay back in, adjusted to the drawing, drilled the stay for the pin, fluxed a pin and set it lightly. I checked against the picture, made some adjustments, drilled for the second pin, fluxed the pin and set it. I checked against the drawing one more time, clamped the piece in my stand, and proceeded to braze it up with brass. I got a clear visual of the brass pulling through and the outer joint was pretty clean so I left it to cool.

When I checked against the drawing, I was spot on. I'm a little surprised by that one.

After this, I started work on a practice fork. Actually, if it comes out well it'll go on my current bike (12 year old trek w/ 3 main tubes in carbon and the rest including the fork in aluminum). I'm sure it's way overbuilt, but I've never fully trusted the aluminum fork. Forks are one of those things that I just don't think should be made of aluminum.

Anyway, I have a Walter (which I suspect is a Long Shin or Everest) crown. It's the ultimate cheater's crown. The rake is built in (7 degrees), the brake-holes are dimpled, there's an internal seat for the steering tube, it's hollow so the fork legs don't need a vent hole, and there is a hole on the underside which can be tapped for a fender or rack and which serves as an additional vent hole. Meanwhile I have some nice but problematic fork tips from Bringheli. They are stainless and look very nice. The fit internally to the tube and have a platform on the end above which a central stub projects. So, it's very easy to set a coil of silver on the end and push the tip into the tube for brazing.

There's just one thing, the tips are pretty big around. I trimmed the fork legs from the bottom exclusively and I still had to grind down the bore of the tip to get it into the fork. This is a slightly tedious process of checking and fitting and checking and fitting. It would probably be a great use for a lathe.

The tips have one other nice feature. On the inner side, there is a hole drilled through the bevel (or arch) between the tip itself and the body that goes up into the the fork leg. This hole goes all the way through the stub at the back end of the tip. So, there is no need to drill a lower vent hole either.

Assuming that one fits the tips correctly to the tubes, it should be a simple matter of checking the leg lengths for equality before brazing the legs to the crown.

Life, however, is not without its challenges. I'm not sure if the crown is straight. Its hard to tell because it doesn't have any straight surfaces on it. I tried laying the steerer on v-blocks, squaring the face of the fork into a vertical plane, and then squaring against the bottom tips of the fork leg sockets. This shows a discrepancy. However, I'm not sure that the crown is that precisely and symmetrically made. I think I'm going to have to face the crown and try to square against the face while holding the steerer in the v-blocks.

Meanwhile, a dry assembly of the fork w/ a wheel indicated that the legs were equal length. So, I thought I'd install the tips. All went well with this process until things were cooled down. Then I found:
  • 2 very small dimples in the fill between the leg and tip on one side.
  • 2 tips twisted relative to the leg, one slightly and one majorly, but both significantly.

This was after I'd finished filling down the first joint. I guess I'll have to reheat the joints and try to slip them into their proper position. First I'm trying to thing of some kind of marking I can use to sight whether the tip is straight or not.

I would have continued working tonight to get the tips right, but I've finally run through my first tank of Oxygen. I'll have to get a refill this week. Meanwhile, I have time to consider how to mark the tip orientation.

Stay tuned for more adventures.

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